The present invention relates to polyolefin lubricant systems and polymer composites containing such polyolefin lubricants. More particularly, the invention is directed to the use of polyolefin or polyolefin/polytetrafluoroethylene blends as lubricants in polymer matrices to provide greatly improved friction and wear properties in the polymer composites.
It is known that various solid and liquid lubricants can be dispersed in a polymeric matrix by melt mixing for the purpose of reducing the coefficient of friction, increasing the wear resistance and increasing the limiting pressure velocity (LPV) of the resulting polymer composite. For example, U.S. Pat. No. 2,855,377 teaches that the incorporation of molybdenum disulfide lubricant particles in polyamides results in a lowering of the coefficient of friction. Similarly, U.S. Pat. No. 3,287,288 teaches that the addition of degraded polytetrafluoroethylene particles to a resinous binder, including a variety of thermoplastic polymers, thermosetting polymers and rubbers, reduces the surface friction of the parent plastic material which may be used to form bearings or similar items.
U.S. Pat. No. 3,458,596 teaches that the addition of discrete, identifiable particles of polyolefin having a molecular weight greater than 500,000 to polyamides and polyacetals results in improved wear resistance and lowered coefficients of friction only if discrete particle phases are preserved during processing (melt mixing). As used herein, the term "molecular weight," will be understood by one skilled in the art to mean weight average molecular weight.
To our knowledge, polyolefins having a molecular weight lower than about 500,000 or polyolefins in which the particles do not remain as discrete particles after processing have not previously been recognized as lubricants for polymer matrices or as providing improved friction and wear properties to polymer composites.